1. Field of the Invention
The invention concerns generally apparatus for wrapping insulation about a conductor bar and particularly, compound-curved conductor bars.
2. Description of the Prior Art
Windings of large electric machines are frequently constructed from coils or bars with rectangular cross section. The quality of the insulation of the coils or bars is a parameter important to the overall quality of the machine. Typically, the insulation of the windings is accomplished by means of tapes of insulating material which are wound on a supply reel and which are wound, at least one layer thick, onto the bars or coils in spiral fashion, with prescribed overlap as well as with sufficient tension.
The wrapping of such conductor bars was formerly done, generally, by hand. A skilled winder was able to adapt to the strength properties of different composite insulating materials by feel. He could also adjust himself to the different geometries of the bars to be insulated. The quality of the insulation was therefore dependent on the craftsman-like skill and the experience of the worker. Of course, his output, because of the relative slowness of the method was low. For this reason, motor-driven devices were developed, which resulted in considerably higher speeds.
One of these automated devices was designed to wrap straight sections of bars. It consists, of a winding head which carries a winding ring equipped with supply rolls carrying one or several insulating tapes. The winding ring revolves during the wrapping with a speed of rotation which depends on the feeding velocity of the work piece. It is guided so that its axis of rotation coincides with the axis of the bar. During the wrapping operation, the winding head is guided parallell to the bar axis. The tension, with which the insulating material can be worked, can be adjusted by means of special devices at the supply or guide rolls. Such arrangements for wrapping electric conductor bars with insulating material are not suited, however, for compound-curved conductor bars, since they cannot follow the curvature.
As far as compound-curved bars are concerned, auxilary devices such as templates, guide bars or other duplicating devices have been used to substantially align the axis of the winding ring with the center line of the bar. Such auxiliary devices, however, must be prepared specially for each bar or coil shape. Further these devices do not completely guarantee that the axis of the winding ring is coincident with the center line of the bar for the full length thereof. An occasional tilting of the winding head by additional control mechanism is therefore necessary. Such winding machines offer a suitable approach where a sufficiently large number of coils or bars of the same shape are to be insulated. This condition, however, applies rarely in the construction of large machines, where the number of conductor bars with the same shape is small. The use of templates or duplicating devices is therefore uneconomical in these special cases, not only because of the preparation of the respective bars, cams and the like, but also because of the relatively high expense of storing them. This is not inconsiderable when one considers the dimensions of windings common in the construction of large machines.
The duplicating and/or template method also has an inherent disadvantage in that they assume a conductor bar or a coil has been made ideally as far as the geometric dimensions are concerned. However, as a practical matter this is not always the case, particularly with the present, manual fabricating methods. With increasing size of the conductor bars, this becomes more of a problem. This fact also makes a duplicating method employing computer "software", such as a prepunched tape, as a template somewhat impractical.
Another known technique uses the conductor bar itself as the template, guiding the winding head along the bar with positive contact. This arrangement, however, results in increased mechanical stress of the insulation, which typically is not designed therefore. This is particularly true of the lower layers, in the case of compound-curved conductor bars. This problem arises due to the fact that the heavy windng head is supported by the insulating tapes. In addition to the static load, acceleration forces come into play. The advancing of the winding head, particularly in the region of inclinations, causes additional stresses on the insulating material.
It is therefore a primary object of this invention to provide an apparatus for winding a curved-conductor bar which avoids many of the disadvantages of known devices.